Fix regression in importation of custom lists

Reported by:
- https://github.com/uBlock-user:

Imported custom list were incorrectly seen as out of
date immediately after import operation.

Regression from:
- e27328f931

A few lines of code were improperly removed during
refactoring.

src/js/assets.js

@@ -695,6 +695,12 @@ api.get = async function(assetKey, options = {}) {
             ? await api.fetchFilterList(contentURL)
             : await api.fetchText(contentURL);
         if ( details.content === '' ) { continue; }
+        if ( reIsExternalPath.test(contentURL) && options.dontCache !== true ) {
+            assetCacheWrite(assetKey, {
+                content: details.content,
+                url: contentURL,
+            });
+        }
         return reportBack(details.content, contentURL);
     }
     return reportBack('', '', 'ENOTFOUND');

src/js/storage.js

@@ -268,9 +268,9 @@
     }
     const newSet = new Set(newKeys);
     // Purge unused filter lists from cache.
-    for ( let i = 0, n = oldKeys.length; i < n; i++ ) {
+    for ( const oldKey of oldKeys ) {
-        if ( newSet.has(oldKeys[i]) === false ) {
+        if ( newSet.has(oldKey) === false ) {
-            this.removeFilterList(oldKeys[i]);
+            this.removeFilterList(oldKey);
         }
     }
     newKeys = Array.from(newSet);